[tsimionescu]

Oh, understood, the housing will "trickle down", right?

How many times do we need to learn that trickle down economics doesn't work? Making the rich richer and happier will never "trickle down" to the poor, it will stop at the rich.

With land, this is particularly obvious. There is a finite amount of land. The more of it is occupied with luxury mansions, the less land will be available for high-density housing. Building 1 new luxury mansion removes land from the pool that could house dozens if not hundreds of people. And rich people don't move in from cheaper housing to more expensive, they just keep both, or they buy the new mansion as a vacation home.

Property is an investment, and there are huge vested interests in keeping property values going up - and not just from rich people, but virtually everyone who owns their own home. You have to fight a lot of these interests to force prices to go down. "Just build more" doesn't work, the space in and around a city is limited.